Electrical Double Layer as a Model of Interaction between Cellulose and Solid Acid Catalysts of Hydrolysis

Abstract

Solid acid catalysts of cellulose hydrolysis in aqueous media attract considerable research interest because of the ease of their separation from the reaction products. The nature of interaction between the two solids is a relevant topic of ongoing research. One aspect of behavior of solid acids in water was not previously discussed in literature with regard to hydrolysis of cellulose: electrolytic dissociation and formation of electric double layers. In this work, on theoretical level, we consider the role of the double layer created by the solid acid when cellulose hydrolysis takes place. The diffuse layer of protons is regarded as the medium where the hydrolysis reaction occurs. Protonation of cellulose by these protons imparts positive charge onto its surface, and cellulose is electrostatically attracted to the polyanion of the catalyst. Thus, the two solid surfaces stay close to each other despite Brownian motion; this allows explaining the high activity of solid catalysts even when chemisorption of carbohydrates on a catalyst is not favorable.

Unidimensional Approximation of the Diffuse Electrical Layer in the Inner Volume of Solid Electrolyte Grains in the Absence of Background Ions

“…If a double layer formed by dissociation of a solid electrolyte surface can be represented or approximated as spatially unidimensional, then a previously reported method for calculation of double layer configurations can be employed. [20] In short, the solution of any such problem must satisfy the mass balance (the amounts of ions in the diffuse layer and the counter-ions in the dissociated solid must be equal. Also, dissociation equilibrium must be maintained in every point of the system).…”

“…Although this concept is equally suitable for any kind of electrolyte (acid, base, salt) as long as it can be described with a dissociation equilibrium constant, in this text we will usually refer to a modeled solid electrolyte as acid to keep the terminology and mathematical symbols familiar and consistent with the previous work. [20] Here, a brief summary will be given for the two EDL models studied in this paper. Their detailed mathematical description and the numerical calculation procedure are available in the Electronic Supporting Information.…”

“…[4][5][6] Presently, the theoretical basis for autodissociative EDLs in scientific literature appears to be limited to our aforementioned earlier work. [20] We intend to further develop this theory, and at this time we would like to resolve a couple of questions that can be answered within the same unidimensional approximation as in our initial paper. These address the role of the inner volume of a solid electrolyte particle.…”

“…We proposed the concept of autodissociative EDL as a possible explanation of chemical interaction between solid cellulose and solid acid catalysts of hydrolysis. [20] Using a simple unidimensional model that considers interaction of two flat surfaces, we analyzed the possibility of cellulose hydrolysis by protons of the diffuse layer, assisted by electrostatic attraction between the solid acid polyanion and the cellulose which is protonated by the same protons. Despite the model's simplicity, a number of experimental facts known from earlier literature were successfully explained.…”

“…Despite the model's simplicity, a number of experimental facts known from earlier literature were successfully explained. [20] This suggests that the role of EDLs in catalysis may not be limited to just the aforementioned physical effects like electrocapillarity and viscosity; in fact, a diffuse layer may itself act as a thin layer of effectively homogeneous catalyst.…”